In 2004-05 counts of the bacteria proteolytic, ammonifying, AOB and NOB, NO₃-N to NO₂-N reducing, denitrifying, and atmospheric nitrogen fixing (Azotobacter sp. and Clostridium pasteurianum) were analyzed along with temperature, pH, dissolved oxygen saturation, ammonia, nitrite and nitrate nitrogen in waters of the River Drwęca. The counts of the above groups of bacteria ranged within a few orders of magnitude depending on the physiological group and sampling site. The smallest were the counts of autotrophic nitrifying and atmospheric nitrogen fixing bacteria Azotobacter sp. (10² cfu·1 cm^-3) and Clostridium pasteurianum (10² MPN·100 cm^-3). The most numerous were ammonifying bacteria (10³ – 10⁶ MPN·100 cm^-3). The quantitative occurrence of the bacteria in question varied in relation to the physical and chemical parameters of the water, which was evidenced by Spearman’s statistical analysis.